/**
  * Return the single association referenced join column name (if any).
  *
  * @param string $fieldName
  * @throws MappingException
  * @return string
  */
 public function getSingleAssociationReferencedJoinColumnName($fieldName)
 {
     if (!$this->isAssociationWithSingleJoinColumn($fieldName)) {
         throw MappingException::noSingleAssociationJoinColumnFound($this->name, $fieldName);
     }
     return $this->associationMappings[$fieldName]['joinColumns'][0]['referencedColumnName'];
 }